The present invention relates to an advancement device for step-wise transport of material and/or a workpiece, and which is particularly adapted for use in a press; the advancement device includes two gripper rails spaced from one another, which extend along a transport path. The gripper rails are reciprocally movable together along an advancement direction, while being movable in respective opposite directions along a direction transverse to the advancement direction. Two longitudinal guides receive the gripper rails, respectively, and a transverse drive is provided for driving the longitudinal guides in the respective opposite directions along the transverse direction. An advancement sled is reciprocally movable along the advancement direction, and an advancement drive is provided for reciprocally driving the advancement sled along the advancement direction. The gripper rails are connected to the advancement sled rigidly along the advancement direction, but are movably connected thereto along the transverse direction.
Advancement devices of this type are known, and described, for example, in U.S. Pat. No. 3,011,464 and in German laid-open specification 22 06 407, in which gripper rails spaced from one another and extending along a transport direction are jointly movable reciprocally along an advancement direction, and are driven in a direction transverse to the advancement direction in respective opposite directions by means of rotating cam disks and by means of suitable transfer elements. In view of the precision required for the manufacture and operation of cam disk drives, or for driving of cam disks, such advancement devices are extremely expensive. Since the operating strokes are fixed in the respective directions of movement, once the dimensions of the cam disk drives are set, matching of such drives to any changed operating conditions is not possible, or feasible only at an inordinately high expense.
Thus in an advancement device of the prior art, which is described in German patent DE-AS No. 28 14 118, there is provided a transmission ratio gearing of an adjustable stroke between a cam disk drive and an advancement sled, wherein the latter is reciprocally movable along an advancement direction. This device of the prior art permits a certain change of the operating stroke along the advancement direction within predetermined limits. Naturally an advancement device with a transmission ratio gearing used in the advancement drive is very expensive.